Production of dry sulfur trioxide



Aug. 29, 1950 B. M. CARTER PRODUCTION 0F DRY SULFUR TRIOXIDE Filed May 22, 1946 ATTORNEY Patented Aug. 29, 1950 PRODUCTION oF DRY SULFUR TRIoXIDE Bernard M. Carter, Montclair, N. J., assig'nor to Allied Chemical & Dye Corporation, a corporation of New York Application May 22, 1946, Serial No. 671,577

6 Claims. (Cl. :Z3- 175) This invention relates to improvements in the manufacture of oleum and sulfuric acid.

The invention, its objects and advantages may be understood from the following description taken in connection With the accompanying drawing showing diagrammatically, apparatus in which a preferred embodiment of the improved process for making oleum may be carried out,

Referring to the drawing, numerals II, I2, I3, I4, I5, I6 and I'I respectively indicate a sulfur vaporizer, a combustion chamber, a gas cooler, a lter and three converters of a multi-stage catalytic SO2 oxidation operation. Vaporizer II may be any apparatus adapted to pressure operation such as a stationary unit into which sulfurous material is charged and burned to form SO2 gas or a mixture of SO2 gas and sulfur vapor. Combustion chamber I2 may be of suitable construction by means of which completion of combustion of sulfur is effected. Converters I5, IIi` and I1 may be of any satisfactory design known in the art, the converters each being arranged to contain a catalyst such as a vanadium catalyst the activity of which is not adversely affected by the presence of moisture in the gas stream.

Undried air at atmospheric temperature is supplied to the process by a main blower 20 the pressure side of which communicates thru header 2| and valve controlled pipe 22 with the combustion chamber I2. By valved pipes 24 and 25, air may be introduced into conduits 21 and 28 which connect the converters and thru which the main SO2 gas stream passes from the rst to the second and from the second to the third conversion stages. Some of the air may be drawn from header 2| and forced by booster blower 30 into sulfur vaporizer I I at pressure greater than that at which air is supplied to combustion chamber I2.

The S03 exit gas of converter I1 passes thru line 32 into the gas inlet connection 33 at the bottom of a tower 35 which may be designated as a sulfuric acid condenser and/or a Wet S03 gas drier. Condenser-drier 35 comprises grillework 36 arranged to support packing material 31, a plate 38 for distributing oleum liquor over the packing, and a gas exit pipe 59. Oleum efliuent of tower 35 runs thru pipe 44 into a cooler 45. The suction side of a pump 50 communicates with the outlet of the cooler, and the pressure sideof the pump is connected to pipe I by which oleum liquor may be fed to the top of tower 35 or drawn off thru conduit 53 to a subsequent phase of the process. Cooler 45, pump 50 and pipe connections 44 and 5I may be of any suitable design,

as known in the art, to facilitate control of temperature and quantity of the oleum liquor circulated over tower 35.

In carrying out the preferred embodiment of the invention, brimstone is continuously fed into a pool of molten sulfur maintained in the bottom of vaporizer Il. Admission of undried air at suitable pressure to the vaporizer is adjusted so that part of the sulfur is burned to generate sufficient heat to melt incoming sulfur and to vaporize the unburned balance of the sulfur. The gas mixture leaving the vaporizer is charged into the combustion chamber along with more than enough air from line 22 to effect oxidation of unburned sulfur to SO2. The combustion chamber exit, heated to temperature in the neighborhood of 2000 F., comprises sulfur dioxide, oxygen, water vapor and nitrogen. In this embodiment, operation of the vaporizer and combustion chamber is controlled so as to produce a strong gas containing by volume not less than 10% and preferably not less than 12% SO2. Oxygen content of the gas stream at this point may be in the range of 11 to 9% volume. In cooler I3, the gas stream is cooled down to close to but not below initial conversion temperature, e. g. to T-825 F. If the gas stream contains suspended solids, such as impurities derived from the brimstone, a filter I4 may be employed, and the exit gas thereof, containing (dry basis) say 12% SO2 and 9% oxygen, is introduced into converter I5 at temperature of about 800 F.

The exit of the rst conversion stage may be heated by oxidation reaction to temperature `of about 1160 F. 'and contain (dry basis) about 4.4% SO2, 8.1% S03, and 5.3% oxygen. The converter exit carries a substantial amount of moisture brought into the process with the air and brimstone. Such a gas raises serious operating problems as to possible use between conversion stages of the usual tubular heat exchangers since, when handling a Wet gas, substantial precautions must be taken with respect to heat transferrer design, materials of construction and mode of operation because of the marked tendency of H2804 to condense ont of the gas stream and seriously corrode the transferrers. In the present process, the foregoing difculties are overcome by effecting interstage cooling by means of cool undried air from blower 20 which air has the twofold function of cooling the gas stream down to temperature suitable for admission to the following conversion stage and supplying any additional oxygen needed for completion of conversion. Hence, the valve in line 25 is adjusted soas to reduce the temperature of the gas stream in line El to about 820 F.

rihe gas stream may leave the converter i6 at temperature of about 945 F. and, by regulation of the valve in air line 20, sufcient air may be introduced into conduit 28 to lower the temperature of the gas stream to about 780 F. The gas stream exits converter Il at temperature of about '8'003F ,anda typical converted gas may containby volume '('dry basis) 7.1% S03, 11.0% oxygen, and nitrogen, overall S02 conversion being about 98%. In a representative operation, the converted gas may contain 4,from af16't.o.0.64 gram per cubic foot of H2O, i. e., enough Water to unite with to 40% of'ftheftotal S03 toform H2S04, depending upon geographical-orseasonl able conditions and moisture content of the brimstone. In preferred practicei'ofithe. invention, the S03 gas employed contains preferably not more water than needed to .unite with the 40% of Athe total S03 to form H2S04.

"The foregoing '-usev'or `undried .atmospheric fair ff or -'S02 gas r'formaltionran'd "for .interstage cooling in the catalytic conversion apparatus, 'permits elimination `from the S03 production plant of sulfur rmelting :and gas kdrying equipment and fspecially designed: gas. coolers between Vconversion #stages lHence, capital-investment and mainte- Tnance costsv in'A thisy phase ofioperation' are greatly reduced. However, the f S03 gas formed vand refcoveredin 'conduit32 isa :wet gas and v.thus conftains fpotential `-sulfuric acid 'mist forming con- 7stituen'ts. As 'is .ewell known inl the art; when Yonce wforme'd Vacid fmist cannot 'be removed ffrom 'the `gas fstream 4by normal types :of absorption fprofcedura-goesthru the process :unchanged .and

f v-causes afplantfstack exit orf iiagtwhich at Atimes Fmay v'loe -Iso objectionable Las to :require closing down-'ofthe plant.

iOleum lis customarily :made bycountercurrent 'contact of-SOsgasfand oleum liquor under condi- ItionsC-such'as tofeiffect absorption. of S03 out of the V5gas-'and I to in'crease the dissolVe'dSOs-` content of "the 1 oleum liquor -Vto "make an :oleum product 'of vlsou'ght '5 for `streng-th. Because of th'e high `vapor Lpressure of SOszgas-over o1eum,:a'bsorptionfof l S03 vinfthe:oleumliquorfmust ;be.effected at. relaitivelylow temperatures. .For example, inltypical vpractice ffor making lsay 140% :oleum "from a repliresentative% byvolumeSOs gas, suchSOaigas iislcooleddown fromfthe'OD-SOO" Eksexit tem- :peraturerof 'theSQz converter system to `about 180 F. prior to introductionof .SOsgaslintothe bottomo'ffthepleum production zone, and in the 2manufacture of a20'% .oleumfsuch contact .sys- 'temexitgasis cooled-tofaboutf250 F. Thus,` in any 'case zthe converterfexitgas is:cooled Idown over'such;abroad:temperaturerange that if such 'S03 .gas were .awet gas, intolerablequantties of rsulfuric acid.mist.would be formed, bothzduring .the cooling ofthe'gas and at .thepointiof rst :contact ofltheigas with the -cool oleum'liquo-ln in fthe o'leum production zzone, Hence, the prior '.practicehasrbeen to-iormnJ dry contact system feXit gas, soasto-avoid'lthe acid mist diiiculty, -which operation'requires.theuse in the S03 pro- Vductionaplantuof:tlfievexpensively constructed and frnaintained drying `andheat .transfer equipment.

'The fpresent invention aordsfan 'easily conftrollableproce'dure for makingzoleum'from a .wet :S03.gas,:andaat the `same time'completely elirni- Anettesforat'least reduces 1 the 'formation of acid mistrtofan unobjectionable minimum. The inwentionthus makes it possible .to take ladvantage .of the reduction. of capital .investment and .oper- 'atingscosts permissibleiin. alplant'which produces 4 a wet S03 gas at the exit of the converter system. Practice ci the invention involves contacting the hot wet S03 gas exiting the converter system with oleum liquor under certain conditions of temperature and oleum strength which effect condensation out of the gas stream as H2S04 of all of the H20 contained in the gas stream, bring V'about 'formation or" a substantially dry S03 gas Y'suitable"or'use'in the rproduction of 'oleum, and at the same time minimize formation of acid mist Such operation may be carried out in a packed;Contactingfzone as in tower 55, thru which Zone the S02 gas and dispersed oleum liquor are flowed'infcountercurrent relation. In accordance 4with 'the rinvention, it has been found that the foregoing objects may be accomplished if (ce) :thai/wet S03 :'gas is introduced, at temperature above the dewpoint thereof, into countercurrent 'contact'with oleum. (b) the oleum is maintained at the point of first `contact of oleum with infcomingzwetzgasat .temperatureznot less than 300 and notrmore1than;40 0;F.,.and (c) `the oleum f'fed pto .the contacting zone for the 'contacting operation is'cooier than but .isfoi .substantially :theysame compcsition'as the soleum :discharged irom the contactingr zone. lThus, .the preferred embodiment of the inventioncomprises:continuously introducing :a stream of Wet S03 i.gas, `at temperature above vthedewpoint-ithereo, into a rgas-oleum .liquo` :contacting Zone, zcontinuously :introducing oleum into Ysaid zone, passing "the CII 4igas andzthe oleum thru'theazone in'fcountercur- .rent :flow relation, continuously discharging "oleum fromthe Zone, :cooling the toleum4 andfreintroducing cooledoleum into Athe contacting'zone wvithout Achange of composition, pand .controlling .temperature .and yquantity .of reintroduced oleum vso as'to maintain :the oleumatthepoint oLits qiirst Contact with incoming ,wetrgas 'at tempera- Yture .not :less .than 30.07 and .notfmore tthan ,In Vstarting'up the process-Withmespect to :operzation of the condenseredrier A135 .of the fgdrawing, -thep-system Ycomprising cool-er 45, tower and ,lllefconnections ifi and y5I -isilledwith oleum `of any strength above .the Hsulfuric vacidfrnono- :hydrate point, i. e. `sulfuric acid .containing Aat yLleast lsome dissolved S03, and vpreferably :with oleum -scontaining Ynot Ymore -than about-5% `free S03, i. e. oleum. 'Cooler v45 is zdesignedtto accomplishfany desired degree of-heatiemoval :from the ,contained oleum within the limitsrequired -by operationof Ya particular .tower A-rateofcirculation or" oleumliquorv'over'the tower being regulated `by pump 50. While gas enteringtower .35 thruinlet connection:shouldxbe :at temperature above ,the .dewpointgasa practical :m-atter, temperature should be wellabove the dewpoint, preferably not less than 600 F.,.and ,as afrule in the-range of S-800 F. Counter- :current contacting roi; gasfandoleum' in the packed f contacting zone inthe tower l315 proceeds, dry /S03gaszis dischargedfrom thetop Y.ofthe tower thru pipe :38, and oleum'runs 'outfofthe 'bottom Aofthetovver thru pipe 455 into coolerl.

`Assuming aigiven flowqof'hotfwet S03 gas into `thebottom of tower :35,iin accordance with the "invention it has beenfound` thatfwhenthetemxperature and .quantity "of 4oleum 'fed into'the top of `tower 35 is suchlastomaintain the oleum .at :the point of rstcontactioffoleum with incoming wet gasattemperature-not less than 300 :.F. V.anolrnot more than 400 F. (i. e.-for.practical '.purposes an oleum temperature within theBDO- ';400 F. range inQtower outletpipe :44), and when YS03 in the liquor.

practical minimum of about 0.61.0%

the oleum eiiluent is cooled and returned with- 'out change of composition to the top of tower 35, Vall of the H constituents of the incoming gas condense out as HzSOi, most of the S03 content of the incoming gas over and above that needed to unite with the H20 to form HzS04 is discharged from the top of the tower as a dry S03 gas, and formation of acid mist is prevented or minimized.

When operation is under way, assuming the introduction into the bottom of tower of a wet outlet pipe 44 as indicated, cooling the oleum and Lreturning the cooled oleum without change of composition, all other features of operation of the condenser-drier maintain themselves automatically.

The low temperature limit of 300 F. is needed `to .prevent objectionable formation of acid mist.

Temperature of about 400 F. should not be exceeded in order to retain at least some dissolved The 30G-400 F. temperature range inherently controls the oleum strength in pipe 44, such strength ranging from a maximum vof about 5% for an oleum temperature in the lower portion of the Z300-400 F. range, downto a oleum strength for an oleum temperature in the upper portion of the 3D0-400 F. range. Accordingly, other operating conditions being equal, for a vgiven oleum temperature in pipe4 44, the oleum discharged from the tower thru pipe 44 is main- -tained at a constant composition of relatively low dissolved S03 content.

As this oleum, after cooling, is returned to the top of the tower, it will be seen that the oleum eflluent of the tower and the oleum returned to the tower are of identical compositions, this feature being an important `.distinguishing characteristics of the present process. Since the purpose of operation of the condenser-drier is to make a dry gas having a maximum S03 concentration, it is preferred to operate the contacting zone as hot as possible while still maintaining the circulating liquor above the sulfuric acid monohydrate point. Further, the hotter the liquor effluent in pipe 44 the less is the tendency for acid mist formation.

Taking into consideration the quantity of oleurn circulated over the tower, thecooling effected in cooler need be no more than that necessary to maintain the 30D-400 F. temperature range in tower outlet pipe 44. For a representative commercial size condenser-drier, it is preferred to introduce the oleum into the top of the tower at temperature of not more than 260 F. and usually less. The relation between the temperature of the oleum in outlet pipe 44 and the oleum fed into the top of the tower may be regulated by the amount of heat removal in cooler 45 and by the quantity of acid circulated over the tower.

During descent of the oleum liquor thru the 'upper portion of the contacting zone, oleum strength probably rises appreciably, but because of the increasing temperature gradient between the top and the bottom of the tower the dissolved oleum content decreases back toward the particular composition prevailing in discharge 'pipe 44. It will be understood that the H20 entering the bottom of the condenser-drier unites Vwith suilicient S03 to lform 100% H2S04, and in the lower part of the tower there is a continuous HzSOi formation which would be expected to reduce continuously the dissolved S03 strength of the oleum discharged from the tower. To the contrary, it has been found that the maintenance of the 3D0-400 F. temperature range in `pipe 44 inherently creates in the lower part of the contact zone conditions which cause just enough absorption of S03 to bring the 100% H3S04 up to the existing dissolved S03 working conditions. Accordingly, in the condenser-drier operation as practiced the only overall S03 absorption which takes place is that which forties the 100% H2S04 constantly being formed up to the dissolved S03 content of the tower liquor eluent. 1.

In the contacting zone of tower 35 there `are two principal sources of heat, sensible heat of the hot incoming S03 gas and heat of forma-tionof .sulfuric acid. The condensing-drying operation effected is characterized by the fact that no `net .desorption of S03 takes place in the contacting zone. Hence, there is no heat utilized in causing net S03 desorption and, aside from radiation losses, all of the heat in the contacting zone corresponding Iwith the net difference between the temperature and chemical composition of the gas in inlet pipe 33 and the gas in outlet pipe 39 is removed from the contacting zone by the oleum-and is discharged from the system by the cooling carried out in cooler 45. This heat removal from the contacting zone and avoidance.` of S03 -desorption by such heat removal are automatically taken care of by the single expedient of main- -ture of the oleum in condenser-drier discharge pipe 44 is about 375 F. Hence, the amount, of heat removal in cooler 45 and the rate orioneration of pump 5t are chosen, according to the design of the particular tower being used, to control the temperature and quantity of the `oleum fed into the top of the tower so as to maintain the oleum in pipe 44 at temperature of about 375 F. In this situation, the oleum in pipe. and the oleum fed into the top of the tower contain `about 1.0% by weight of tree S03, i. e.

.1.0% oleum. Temperature of the oleum fed into thetop or" the tower thru pipe 5i may be about 250 F. There is then produced in gas off-take pipe 3S a dry gas having a temperature of about 250 F., and an S03 concentration by volume'of about 5.0%. The make of 1.0% oleum in the .circulating system of tower 35 is run thru line 53 into the cooler 6i of the e. g. 20% oleumproduction tower 62. Design and construction of tower 62 may be ,the same as that of the packed oleum production towers known in the art. This tower includes at the top a gas outlet 64 and an oleum inlet 65, and at the bottom a gas inlet 61 and an oleum outlet ,B8 connected to cooler 6i. The `sulfuric pmocess'. may be drawn off thru pipe. 18' 'gasastreamzleaving the top of'tower' andxpass.-

Introduction of` diluently intocoolerr l fromlines Sand l5', cooling and rate ofV liquor'flow'in-:the

circulatingl system. of tower 62 are regulated: so thattoleum. of strength of about 18% andai; temperature of about 135i F. is fedi intothertop -offtoweir 62.' thru pipe Gas and: liquor contactlng: in tower 32 is such that.' 20% oleumis 'discharged from the bottom' of tower 62.' byy pipe tfroiny which the oleum make of the? entire The ingrfthrmpipe into the bottom ofjsulfuric acid 'production tower lil'rnay be at temperaturefof about 135 F. and have an S03 concentration-by volumefoifabout 2.8%.

Whatever extraneous diluent may be'ne'ededlin theiprocess issintroduced, as water: orf dilute sul'- Ifixricfacid', thru line Si?. into the acid circulating sffstemof` tower l0. rEhe liquor cooling andfcir.-

"culatiug: system of tower i is operated' as' is "Known in the artto produce. say 99% strength "sulfuric aci-d, andthemalie. of towerxlwis passed.' thru: line. E5 into the cooler 64?. of oleum production -tower'` 62;

' The.' proeessras'described up t0 and: including operation of the condenser-drier may belusedin vcormection,with production ofsulfuri'c acidialone .1 ihfawhich instance gas outlet pipe 39nof tower 35 -may beconnected directly to the gasinlet .atnthe bottom of tower i0; and oleum line-53f may he "connected to cooler il of tower 7i). In'this vmodication, the-exit gas' of pipe 39', aty temperature 'of"about.x250 F; and containing 5.0`%by.volume of S03 is introduced into the bottornlofitowerv r'Imirwhichiis :operated as known in the artito'producestrong e; g. 99.5% sulfuricacid. The advantage of' this mode of procedure isthat sulfuricacid may be made from all of the S03 contentof an initially wet S03 gas, byflrst con- 4d'ensing out the H20 of the wet gas as H2S`04, `and then recovering. the'dry S03 as produot'sulfurie` acid. by means of a low temperature S03 -asbsorption step. Since in this operation, tem- "perature of the acid dischargedfroni'the tower 'llllirieedvnotA bel higher than 140 F., it'willi be seenthat corrosion caused by high temperature ist avoided and it is possible to useless expenvsiirely constructed and'inaintained apparatus.

Y Ilelairn:

1; The process for making substantially dry SDaigas from a wet gas containing S03 con- `stituent and some but less H20 constituent than needed to unite with all S03 present in saidwet gas torform H2S04, which process comprises introducing stream of said wet gas, at temperature above the dewpoint thereof, into a gas-oleum l contacting. zone, introducing hereinafter dened oieunr having at least some dissolved'free S03 'into said zone, passing said gas andvsaid'ioleumA vthruLsaid Zone in countercurrent iiow relation,

discharging oleum from said zone, cooling. said 'oleum and reintroducing said cooled oleum into said zone without change of composition, conati'ollngY temperature and; quantity ofi reintroducedoleurn so as to maintain said oleum at vvtl'iex-point'oiiirst contact of oleum'with incomingf wet'gasat temperature not less than 300 andnot'more than 400." whereby H2O is .1 lcondensed. out. of the..v gas; stream yas H2504, and

gas to SCi-in aTv multi-stage conversion operation,

frmationof-.acid mistissrninimized, .and the free SOystrength'oi the oleum discharged from said zonezis-l substantially the same asv the free S03 strength-of the oleum introducedinto saidzone;

andedischarging` substantially dry S03 gasifrom saidzone'.

2. The process. for making substantially dry S03: gas from a wet gas containing S03 constituent and some but less H2O constituent than neededato'unite with allSOa present in saidwet gas todorm H2804, which process comprisesiritroducingv a; streamof said wet gas, at tempera ture'abovethe dewpoint thereof, into agas-oleum Contacting zona: introducing oleum having.V at leastsome dissolved .free S03 into said zone;- passing:.said gas and said oleum thru said zone 1in counterourrent flow relation, dischargingoleum from saidzone, controlling temperature and quantityy of: oleum .introduced into said zone `so lasto `maintain'-saidA oleum at the pointy oi iirst' con,-

tact-ofl oleum with. said incoming wetv gas. at temperaturenot lessthan 300 F. andnot more than 400 F., said oleurn introduced into: said zone being: coolerthan and having thefsame composition as the oleuin discharged from' said zone', Whereb'yI-IzO condensed out offthegas si'f'reain'z as HzSOli and iormationoi acid mist.y is minimized, andthe free SOastrength of the oleum discharged from said zone is substantiallytheV lsaine-sas:the.free S03 strength of the oleumintroducedf into saidl Zone; and dischargingsubstantially dryySOa gas'irom said zone.

3:.Thei process for making substantially:` dry SOag-a'sfrom'a Wet gas containing S03 constit- -uenti andsome but. less H20 constituentk than nee'dedtoxunitewith all S03 present insaid wet gast: tozform H2804, which .process Vcomprises introducing-'a stream of` said wet gas, attemperatureabovethe dewpoint thereof, into a gas-oleum contacting zone, introducing hereinafter defined oleumrhavingat least some dissolved free SO: into said'szone, passing saidgas' and said' oleurn throughsaid. Zone in countercurrent flow relationdischarging. oleum fromsaid zone, cooling saidzoleum tottemperature not' higherthan 260 E:.and.freintroducing saidv cooledoleum intosaid zonewithout change of composition, controlling temperature. and quantity of reintroduced oleum so as: to maintain saidoleum atY the point; of first` contact'A of oleum with incoming" wet gas at?.temperature.notil less than 300 andV not more than 400 F;, whereby H20 is condensed outlof tliegasV str-camas HzSOi and formation of: acidi mist is minimized, and the free S03 strengthof the oleurn discharged from said zone is substantially the saine as the free S03 strength of theoleumintroduced into said zoneyand dis charging substantially dry S03 gas from said zone.

4. The-process: for making oleum which comprisese burning sulfur material with undried: air toxform aihot, moist S02 gas, cooling saidmoist gas to but not belowinitial conversion temperature,1catalytically oxidizing the SOzscf said-moist effectingJ the required. cooling of the gas stream between: stages by introduction between stages ofiundriedair, continuously introducing the rcsulting wet gas containing S03 and H20 constituents, attemperature above the dewpoint theren of, into ar'gas-oleum contacting zone, continuously introducing hereinafter dened oleuin having` at leastsome dissolved free S03 into said zone, passing.l said gas and. said. oleum thru said zonein countercurrent owv relation, continuously discharging oleum from said zone, cooling said oleum and reintroducing said cooled oleum into said zone without change of composition, controlling temperature and quantity of reintroduced oleum so as to maintain said oleum at the point of first contact of oleum with incoming wet gas at temperature not less than 300 F. and not more than 400 F., whereby H30 is condensed out of the gas stream as H2504 and formation of acid mist is minimized, and the free S03 strength of the oleum discharged from said zone is substantially the same as the free S03 strength of the oleum introduced into said Zone; continuously discharging substantially dry S03 gas from said zone, and continuously introducing said dry S03 gas into an oleum production zone regulated to absorb S03 and form oleum.

5. The process for making sulfuric acid which comprises burning sulfur material with undried air to form a hot, moist S02 gas, cooling said moist gas to but not below initial conversion temperature, catalytically oxidizing the S02 of said moist gas to S03 in a multi-stage conversion operation, effecting the required cooling of the gas stream between stages b-y introduction between stages of undried air, continuously introducing the resulting wet gas containing S03 and H20 constituents, at temperature above the dewpoint thereof, into a gas-oleum contacting zone, continuously introducing hereinafter dened oleum having at least some dissolved free S03 into said zone, passing said gas and said oleum thru said Zone in counterourrent flow relation, continuously discharging oleum from said zone, cooling said oleum and reintroducing said cooled oleum into said zone without change of composition, controlling temperature and quan tity of reintroduced oleum so as to maintain said oleum at the point or nrst contact of oleum with incoming wet gas at temperature not less than 300 F. and not more than 400 F., whereby H20 is condensed out of the gas stream as HzSOi and formation of acid mist is minimized, and the free S03 Strength of the oleum discharged from said zone is substantially the same as the 10 free S03 strength of the oleum introduced into said zone; continuously discharging substantially dry S03 gas from said zone, and continuously introducing resulting dry S03 gas into a sulfuric acid production Zone regulated to absorb S03 and form sulfuric acid.

6. The process for making substantially dry S03 gas from a wet gas containing S03 constituent and some but less H20 constituent than needed to unite with all S03 present in said wet gas to form H2S04, which process comprises introducing a stream of said wet gas, at a temperature not less than 600 F., into a gasoleum contacting zone, introducing hereinafter defined oleum containing at least some but not more than about 5% free S03 into said zone, passing said gas and said oleum through said zone in countercurrent flow relation,` discharging oleum from said zone, cooling said oleum to temperature not higher than 260 F. and reintroducing said cooled oleum into said zone without change of composition, controlling temperature and quantity of reintroduced oleum so as to maintain said oleum at the point of rst contact of oleum with incoming wet gas at temperature not less than 300 F. and not more than 400 F., whereby H30 is condensed out of the gas stream as Il-IzSOi and formation of acid mist is minimized, and the free S03 strength of the oleum discharged from said zone is substantially the same as the free S03 strength of the oleum introduced into said Zone; and discharging substantially dry S03 gas from said zone.

BERNARD M. CARTER.

REFERENCES CITED The following references are of record in the ile of this patent:

UNITED STATES PATENTS Number Name Date 1,233,627 Weber July 17, 191'? 1,896,287 Clark Feb. 7, 1933 2,042,675 Merriam June 2, 1936 2,199,691 Carter May 7, 1940 

1. THE PROCESS FOR MAKING SUBSTANTIALLY DRY SO3 GAS FROM A WET GAS CONTAINING SO3 CONSTITUENT AND SOME BUT LESS H20 CONSTITUENT THAN NEEDED TO UNITE WITH ALL SO3 PRESENT IN SAID WET GAS TO FORM H2SO4, WHICH PROCESS COMPRISES INTRODUCING A STREAM OF SAID WET GAS, AT TEMPERATURE ABOVE THE DEWPOINT THEREOF, INTO A GAS-OLEUM CONTACTING ZONE, INTRODUCING HEREINAFTER DEFINED OLEUM HAVING AT LEAST SOME DISSOLVED FREE SO3 INTO SAID ZONE, PASSING SAID GAS AND SAID OLEUM THRU SAID ZONE IN COUNTERCURRENT FLOW RELATION, DISCHARGING OLEUM FROM SAID ZONE, COOLING SAID OLEUM AND REINTRODUCING SAID COOLED OLEUM INTO SAID ZONE WITHOUT CHANGE OF COMPOSITION, CONTROLLING TEMPERATURE AND QUANTITY OF REINTRODUCED OLEUM SO AS TO MAINTAIN SAID OLEUM AT THE POINT OF FIRST CONTACT OF OLEUM WITH INCOMING WET GAS AT TEMPERATURE NOT LESS THAN 300* F. AND NOT MORE THAN 400*F., WHEREBY H2O IS CONDENSED OUT OF THE GAS STREAM AS H2SO4 AND FORMATION OF ACID MIST IS MINIMIZED, AND THE FREE SO3 STRENGTH OF THE OLEUM DISCHARGED FROM SAID ZONE IS SUBSTANTIALLY THE SAME AS THE FREE SO3 STRENGTH OF THE OLEUM INTRODUCED INTO SAID ZONE; AND DISCHARGING SUBSTANTIALLY DRY S03 GAS FROM SAID ZONE. 